This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-178191 filed on Jun. 14, 2000 and Japanese Patent Application No. 2001-151042 filed on May 21, 2001.
1. Field of the Invention
The present invention relates to a transformer device, to a high-voltage generating apparatus having the transformer device received in a metal case, and also to a lighting system having the high-voltage generating apparatus.
2. Description of Related Art
In order to turn on a discharge lamp of a lighting system, a high voltage (e.g., about 20 kV) needs to be applied between electrodes of the discharge lamp. In a transformer device that generates such a high voltage, a voltage to be applied to a primary coil is rapidly switched by a control circuit to generate the high voltage in a secondary coil. A high-voltage generating apparatus includes such a transformer device received within a metal case. In the high-voltage generating apparatus, there are high-voltage portions and low voltage portions. The high-voltage portions include, for example, a high-voltage side end of the secondary coil and a high-voltage terminal electrically connected to the high-voltage side end of the secondary coil. The low-voltage portions include, for example, the metal case, which receives the transformer device, and the control circuit. An electrical discharge (leakage) can take place between the high-voltage portion(s) and the low-voltage portion(s), causing some undesirable results, such as, damage to the control circuit, reduction in the voltage of the secondary coil, or the like.
In order to prevent the electrical leakage between the high-voltage portion(s) and the low-voltage portion(s), a dielectric resin material can be filled around the primary coil and the secondary coil in the transformer device. However, the step of filling the resin material needs to be added to the manufacturing process, resulting in an increase in a manufacturing cost. Alternatively, a space between the high-voltage portion and the low-voltage portion can be increased. However, this normally causes an increase in a size of the high-voltage generating apparatus.
FIG. 17A shows one previously proposed high-voltage generating apparatus 500 having a transformer device 510 received within a metal case 540. The transformer device 510 includes a core 511, a secondary coil 512 wound around the core 511, a dielectric resin housing 520 receiving the core 511 and the secondary coil 512, and a primary coil 513 wound around the housing 520. A high-voltage side end of the secondary coil 512 is connected to a high-voltage terminal 515 to output a high voltage generated in the secondary coil 512 from the transformer device 510. One end of the housing 520 where the high-voltage side end of the secondary coil 512 and the high-voltage terminal 515 are present is open. Thus, once the transformer device 510 is installed within the metal case 540, electrical leakage similar to that described above can take place between the high-voltage portions of the transformer device 510 and the metal case 540 that acts as the low-voltage portion. In order to restrain the electrical leakage between the high-voltage portions of the transformer device 510 and the metal case 540, the high-voltage portions of the transformer device 510 is covered with and received within first and second resin cases 530, 535 that are engaged with each other to provide a substantially closed space therebetween.
As shown in FIGS. 17A and 17B, when an engaging portion 536 of the second resin case 535 is engaged with an engaging portion 531 of the first resin case 530, a maze structure is formed. Because of the maze structure, a creeping distance between the high-voltage portions of the transformer device 510 and the metal case 540 is increased. Thus, the maze structure formed with the first and second resin cases 530 and 535 restrains the electrical leakage between the high-voltage portions of the transformer device 510 and the metal case 540.
However, the presence of the resin cases 530, 535 between the high-voltage portions of the transformer device 510 and the metal case 540 results in an increase in the number of components to be assembled and also results in an increase in a size of the high-voltage generating apparatus 500.
Thus, it is an objective of the present invention to provide a compact transformer device, which can be readily manufactured with a reduced number of manufacturing steps and can restrain the electrical leakage. It is another objective of the present invention to provide a high-voltage generating apparatus including such a transformer device. It is a further objective of the present invention to provide a lighting system having such a high-voltage generating apparatus.
To achieve the objectives of the present invention, there is provided a transformer device including a housing made of a dielectric material, a core received within the housing, a secondary coil wound around an outer peripheral surface of the core, a high voltage terminal, and a primary coil electromagnetically coupled with the secondary coil for generating the high voltage in the secondary coil. The secondary coil has a high-voltage side end from which a high voltage is outputted. The high-voltage terminal is connected to the high-voltage side end of the secondary coil to output the high voltage from the transformer device. The housing has an open axial end and a closed axial end. The high-voltage side end of the secondary coil is positioned within the housing adjacent to the closed end of the housing.
Furthermore, there is provided a high-voltage generating apparatus including the transformer device and a metal case that receives the transformer device. The metal case is arranged adjacent to the housing of the transformer device.
Also, there is provided a discharge lamp lighting system including a discharge lamp and the high-voltage generating apparatus. The high-voltage generating apparatus is electrically connected to the discharge lamp for generating a high voltage to be supplied to the discharge lamp to turn on the discharge lamp.